1. Field of the Invention
The present invention relates to the production of polyolefin nanocomposites, and particularly to the use of an aluminum nitride (AlN) nano-filler as a promoter of olefin polymerization with a metallocene catalyst.
2. Description of the Related Art
Polyethylene (or polythene) is the most widely used plastic, with an annual production of about 80 million metric tons. Without the usage of conversion catalysts, polyethylene manufacture is relatively difficult. A chromium trioxide-based catalyst, referred to as the Phillips catalyst, was first discovered in the early 1950's, and a catalytic system based on titanium halides and organo-aluminum compounds that worked at even milder conditions than the Phillips catalyst was developed later in the decade. These catalysts are referred to as Ziegler-type catalysts. The Phillips catalyst, however, is less expensive and easier to work with, and both methods are still used in industrial practice.
A third type of catalytic system, one based on metallocenes, was discovered in the 1970's. The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low density polyethylene and linear low-density polyethylene. Such resins have begun to replace aramids in many high-strength applications.
Given the advantages provided by metallocene catalysts, it would be desirable to develop a metallocene catalyst-based method for polymerizing ethylene with an optimal conversion activity. Metallocene catalysts provide certain flexibility with respect to activity, particularly in comparison to Ziegler-Natta catalysts. This is possible due to the addition of fillers, which act as promoters to the catalyst. Although various fillers have been experimented with in recent years, several problems still exist in their use. Difficulties in controlling polymer morphology with soluble catalysts have been encountered, along with the necessity of using relatively large amounts of co-polymers to achieve maximum catalytic activity. It would obviously be desirable to find a filler that easily controls polymer morphology, but does not require large quantities of co-polymers to be used, and which further enhances the overall properties of the resultant polyethylene composites.
Thus, a method of making polyolefin nanocomposites solving the aforementioned problems is desired.